Photon and electron racing show

Say I was watching a photon and an electron are racing (ignore other physics factors), the photon is moving away from the electron at a constant speed, v.

Since the show plays too fast for me, so I slowed down the movie and re-watch the show again.

In common sense, both electron and photon will be slowed down by equal proportional ratio respectively and the velocity v too. The result is photon moves away from electron but slower.

For another case, electron is slowed down as before, but for photon it maybe just red-shifted instead of slowing down. The result is, velocity v increase and the photon moves faster away from the electron.

Instead of expanding Univrse, is it relevant to taking account of if our Universe had gradually slowing time? I mean the "expandind" of Universe is maybe just relative effect on our understanding of what we had measure to the slowing time effect? Maybe there two answers in one question.

Staff: Mentor

AlienUFO said:

Say I was watching a photon and an electron are racing (ignore other physics factors), the photon is moving away from the electron at a constant speed, v.

Realizing that this is just an amusing thought experiment (lots of luck "viewing" a passing photon), from your inertial reference frame the electron is moving at some speed v while the photon moves at speed c. From your frame, the photon gains distance on the electron at the rate "c - v". From the electron's frame, the photon moves at speed c.

Since the show plays too fast for me, so I slowed down the movie and re-watch the show again.

In common sense, both electron and photon will be slowed down by equal proportional ratio respectively and the velocity v too. The result is photon moves away from electron but slower.

So? While you're at it, why not take a pretend snapshot, in which case photon and electron will both be at rest. What's the point?

For another case, electron is slowed down as before, but for photon it maybe just red-shifted instead of slowing down. The result is, velocity v increase and the photon moves faster away from the electron.

Realizing that this is just an amusing thought experiment (lots of luck "viewing" a passing photon), from your inertial reference frame the electron is moving at some speed v while the photon moves at speed c. From your frame, the photon gains distance on the electron at the rate "c - v". From the electron's frame, the photon moves at speed c.

Well then, is there any problem?

Doc Al said:

So? While you're at it, why not take a pretend snapshot, in which case photon and electron will both be at rest. What's the point?

I don't know if you really don't understand my question or I am describing something wrong. Why must take a rest frame between photon or electron? Maybe I'll make it clearer: First, "Say I had recorded a racing show between photon and electron, I can see that photon and electron is moving with their velocities respectively, I see photon is moving away from electron with a velocity", and then, "I watch the show again and but this time I let the show plays slower, now I see the photon is still moving away from electron but this time it is moving away slower then before (the photon and electron is moving slower as I watch the slowed show this time)"

Actually, there is a big difference which I set-up onto relativity I know, which is I let the time become variable, which mean that if I can slow down the time clock to see if there is something act different. So I came up with another speculation thought: "For another case, if I watch that slowed movie play, the electron will move slower but the photon won't (red-shifted), and thus photon will move away from electron faster" which is oppose the result above.

Doc Al said:

Huh? If you have a question, try to rephrase it.

Sorry, there is some mistake:

AlienUFO said:

...but for photon it maybe just red-shifted instead of slowing down.

Yes, I make the sentence confusing. You see, the "photon is slowing down" I mean here is the consicounce of "slowed movie show". "Photon is red-shifted instead of slowing down" is the way I think that when we apply varieties of time speed, photon will not "slows it speed" but red or blue shifted (but is not same as blue-shifted by gravity).

I am sorry for that because I am not honest with my question... well one thing I didn't mention here is my thought on "expending universe". With idea above, maybe we can say "the universe is slowing down instead of expending". I think that weither the Universe is expanding or slowing down, both are explaining red-shift effect, but make no difference. (And that's why I kept the question unclear)

I just wanted to ask, if this is posible? My another porpose is to learn more about relativity.